Apparatus for testing magnetizable workpieces



Dec. 21, 1937. E. SCHWEITZERET AL 2,103,224

APPARATUS FOR TESTING MAGNETIZABLE WORKPIECES Filed May 22, 1955 5Sheets-Sheet 1 Fig.2 I

AMPLIF/Ea 1937- I E. SCHWEITZER ET AL 2,103,224

APPARATUS FQR TESTING MAGNETIZABLE WORKPIECES Filed May 22, 1935 3Sheets-Sheet? Fig.5

6 H E c K JMPZ/F/EZ r I A l I .ATTORNEY3.

' Dec. 21, 1937.

' APPARATUS FORTE-{STING MAGNETIZABLE 'WORKPIECES Filed May 22, 1935 3Sheets-Sheet 3 ATTORNEY8.

. rs. SCHWEITIZERI ET AL 2,103,224 I Patented Dec. 21, 1937' APPARATUSFOR TESTING MAGNETIZABLE WORKPIECES Eugen Schweitzer,Wlesbaden-Biebrlch, and

Siegfried Kiesskalt, Frankfort-on-the-Main- Hochst, Germany, assignorsto I. G. Farbenindustrie Aktiengesellschaft, Frankfort-onthe Main,Germany Application May 22, 1933, Serial No. 672,306 In Germany May 23,1932 2 Claims. (or. 175-183) The present invention relates to anapparatus for discovering inhomogeneities or defects in magnetizableworkpieces, especially in welded seams.

According to our present invention we take advantage of the fact thatthe lines of magnetic force in aworkpiece magnetized in a directionworkpieces at the defective partsfor discovering the location of theinhomogeneity or defective part. According to this known method, the

workpiece to be tested is magnetized by means of an electromagnet and.an induction coil is placed on the surface of the workpiece. Wheneverthe current exciting the electromagnet is switched on and oif, a currentis induced in the coil if the coil is intersected by the lines of mag-25 netic force projecting from the workpiece at the defective parts.(See W. Gerlach, Metallwirtschaft, VIII, vol. 36, pages 875-877,September 1929.)

According to our present invention the known method is considerablysimplified and made the basis of a useful industrial process for thecontinuous testing of magnetizable pieces. Our-new process comprisescontinuously magnetizing-the workpiece to be tested by means ofpermanent 35 magnets or electromagnets or in another manner in adirection parallel with the surface and causing the coil .to oscillatequickly.

For instance, a coil preferably of rectangular shape, with or without aniron core (see Fig. 3) is mounted on a tuning fork so that it oscillatesat the same frequency as the tuning fork and in a direction parallelwith the surface of the workpiece to be tested, when the tuning fork isstruck, said workpiece being magnetized as described above. When thecoil thus oscillating is passed over an inhomogeneous portion of theworkpiece, inductive currents are produced in the coil because of thecutting of lines of magnetic force projecting from the workpiece at thesaid defective part by the coil. These inductive currents can be madeperceptible in a suitable manner, for instance by conducting them overan amplifier to a telephone, a loudspeaker or an earphone in whichaudible sounds are thus produced as soon and as long as the oscillatingcoil' is near the defective part-of the workpiece being tested.

The principle of the invention thus described permits of variousmodifications as to the steps to be taken for causing the coil tooscillate and as 5 regards the method of rendering perceptible thecurrent induced in the coil when the latter is brought in proximity tothe defective arts of the workpiece being tested. I

Instead of connecting the coil with a tuning fork, as above mentioned,it can be placed on an oscillating metal spiral, for instanceon thefirst or second internal turn of a helicoidal clock gong, so that thewinding plane of the coil is parallel with the spiral plane of the-gong.4

The oscillations of the testing coil may also be produced by chargingthe exciting coil of a loudspeaker system directly with ,an alternatingcurrent. For this purpose there may be used the usual industrialalternating current of the supply net work. It is, however, alsopossible to produce the alternating current by using a tube apparatussuch as the ultra-audion connection.

The whole apparatusis small, handy,and can readily be made in the formof a testing body 5 with which joints or junctions in iron constructionscan be approached.

We have succeeded in testing even large and thick parts of welded seamsby means of our device. With it, it is possible todiscover not onlyhollow places, but also those parts which have been welded with anexcess of oxygen, that is, which have been slightly burnt. For instancetwo iron plates of 400 x 400 x 15 mm. were welded together at one oftheir edges so as to form a plane; the welded seam, therefore had alength of 400 mm. 100 mm. thereof were welded as well as possible, 100mm. with small hollow places, further 100 mm. with asmall access ofoxygen and the remaining lQOAmm. were 40 again well welded. The twodefective places could be directly discovered with a device ac-. cordingto the invention. Upon bringing the testing coil to the defectiveplaces, a sound be came audible in the earphone, whereas no sound washeard when the testing coil was passed over the places of the weldedseam which were free from defects, or over the surface bf the two ifonplates. 'The testing operation at the welded seam is not impeded by themagnets 60 placed on the plate. The position of the magnets, can beeasily altered.

It is not necessary to retain -the testing coil in the centre or in themiddle plane of the magnets; only the area immediately surrounding thelines of force.

Fig. 2 shows a coil adjacent the workpiece of Fig. l for testing theworkpiece according to the known process as described by W. Gerlac h inMetallwirtschaft, VIII, vol. 36, pages 875-877,

Sept. 1929.

Fig. 3 is a diagrammatic illustration of an apparatus according to ourinvention.

Fig. 4 illustrates a modification for supporting the coil for,oscillating movement.

Fig. 5 illustrates an arrangement of the testing 'coil working withalternating current.

Figs. 6 and 7 illustrate the oscillating system of Fig. 5 on an enlargedscale.

Fig. 8 shows an arrangement for magnetizing the workpiece with a minimumof disturbances to the testing device.

In Fig. 1, A is a cross section of a magnetizable workpiece containingthe defective part B at which the lines of magnetic force are deflectedupwardly and downwardly, so that they project from the surface of theworkpiece.

According to the method of Gerlach, referred to above, C, in Fig. 2, isthe coil intersected by the lines of force deflected at the defect placeB. By switching the magnetizing current on and off, an inductive currentis produced in the coil C.

In Fig. 3, coil C, preferably of rectangular shape, with or without aniron core, is moimted on a tuning fork D so that it'oscillates with thesame frequency as the tuning fork and in a direction parallel with thesurface of the workpiece A to be tested, when the tuning fork is struck.The coil may be attached to the tuning fork in any suitable manner, onesuitable form of connection being illustrated in the form of anglemembers R secured to the fork and coil.

When the coil C thus oscillating is passed over oscillating coil C isnear the defective place B of the workpiece being tested.

Instead of connecting the coil with a tuning fork, it can be placed onan oscillating metal spiral, for instance on the first or secondinternal turmof a helicoidal clock gong, as illustrated in Fig. 4, sothat the winding plane of the coil is parallel with the spiral plane ofthe gong.

In the device shown in Fig. 5, A is a cross section of an iron piececontaining the welded seam J. G and H are electromagnets placed on theiron piece at both sides of the welded seam. K is the loudspeaker coil,charged with alternating current and containing in its interiorthe coreL which is caused ltooscillate by the alternating current. Theoscillations of this core are transmitted to the testing coil C throughthe arm N which is made of a non-magnetizablematerial. If theoscillating testing coil C is brought to an inhomogeneous part of thewelded seam J,"inductive currents are produced therein which areamplified by the amplifier E and rendered audible in the earphone F.

The oscillating system of Fig. 5 is illustrated on an enlarged scale inFigs. 6 and 7. K is the loudspeaker coil traversed by alternatingcurrent.

The oscillating core of this coil is connected with one end of an arm N.'At the other end of the arm N is the testing coil-C- M is a horseshoemagnet between the poles of which the coil K is placed.

In Fig. '8 there is illustrated the exciting of the magnetic field, inorder to avoid any disturbances. Two separate bar magnets G and H areplaced upon the workpiece A which contains a joint or welded seam J.Only the lower parts of the relatively long bar magnets are within themagnet winding; the upper parts extend very far outwardly and areprovided at their ends with iron handles. By means of this arrangement,the area surrounding the welded seam J to be tested is almost entirelyfree from the magnetic stray field of the poles in spite of thenonclosed magnetic circuit, Because of the fact that the long ,ends' ofthe bars extend upwardly, the stray field is brought to a higherposition and, at the same time, the magnetic resistance is considerablyreducedby their large surfaces, so that the magnetic fiux in theworkpiece still remains. -sufiiciently great.

The small remainder of the strayfield can be rendered inofiensive byplacing two testing coils C on the arm instead of only one. (Figs. 5,- 6and 7.) The two coils are placed directly onebes'ide the other, so thatthey perform exactly the same oscillations, but they have to beelectrically counter-connectedl It is, of

.course, also possible to record the current induced perceptible thecurrent produced in the inductive coil.

2. An apparatus for discovering inhomogeneities in magnetizableworkpieces which comprises a magnet for m'ag'ntizing the workpiece, anin-' ductive coil to be placed in inductive relation to the workpiece,an'arm on which the inductive coil is placed, a coil traversed byalternating ',current and containing an iron core connected with thearm, and an earphone connected with the coil. 3

EUGEN SCHWEITZER.

SIEGFRIED KIESSKALT.

